The party of Pakistan's former PM Benazir Bhutto has said hundreds of its members were arrested overnight ahead of a planned mass rally on Friday.

Activists were taken from their homes in the latest crackdown under emergency rule measures brought in on Saturday by President Pervez Musharraf.

The raids came hours after US President George W Bush told Gen Musharraf in a "frank" phone call to hold polls soon.

Bush told Gen Musharraf he could not be both army head and president.

Bhutto's Pakistan People's Party (PPP) is planning a huge public rally in Rawalpindi, close to the capital, Islamabad, on Friday.

Party spokeswoman Farzana Raja told Reuters news agency there had been mass detentions overnight in central Punjab province.

'Suicide attacks'

Bhutto had earlier insisted the rally would go ahead despite an official ban and called for a "long march" next week unless Gen Musharraf changed course.

She is insisting that he restore the constitution, hold elections and resign as head of the army.

Bhutto is also demanding the release of lawyers, judges and activists detained in the past few days.

The authorities have warned that police will not allow the demonstration to go ahead.

Rawalpindi mayor Javed Akhlas said: "We will ensure that they don't violate the ban on rallies, and if they do it, the government will take action according to the law."

He told the Associated Press there was a "strong threat" of another suicide bomb attack against Bhutto, who survived an assassination attempt in Karachi on 18 October that killed more than 140 people.

Protests, since emergency rule was brought in, have been limited but correspondents say the Rawalpindi rally could raise the stakes dramatically in the country's political crisis.

Musharraf said he declared the state of emergency because of a crisis caused by militant violence and an unruly judiciary.

'Indispensable ally'

Bush said he had spoken to Gen Musharraf by phone for 20 minutes.

"My message was that we believe strongly in elections and that you ought to have elections soon and you need to take off your uniform," Bush told reporters.

"You can't be the president and the head of the military at the same time, so I had a very frank discussion with him."

But Bush also noted that Gen Musharraf had been an "indispensable ally".

PHOTO CAPTION

Pakistani riot police stop supporters of former Pakistani Prime Minister Benazir Bhutto during a protest in front of the President House in Islamabad. [AFP]

BBC (summarized)